Study of device characteristics of intrinsic Josephson junction terahertz emitters related to annealing conditions of the crystals (vol 133, 163904, 2023)

We fabricated terahertz (THz) wave emitters from high-temperature superconductor Bi2Sr2CaCu2O8+d (Bi2212) single crystals annealed under oxygen gas (O-2) flow and nitrogen gas (N-2) flow conditions. To better understand the annealing effects of the crystal for the device, we evaluated both device properties and a c-axis lattice constant using x-ray diffraction. Compared to the N-2-annealed sample, the O-2-annealed sample shows higher critical current in the current-voltage characteristics and no clear emission. In addition, multiple hysteresis loops were observed above 75 K. Based on the x-ray diffraction measurements, it is suggested that the presence of multiple hysteresis loops observed in the I-V characteristics of the O-2-annealed sample is caused by the existence of layers that have varying levels of oxygen content along the c-axis direction of the crystal. The formation of these layers is attributed to the deposition process of metallic thin films during the device fabrication procedure. This result indicates that the Bi2212 crystal surface of the O-2-annealed sample is more sensitive than that of the N 2-annealed one. The information is useful for preparing the Bi2212 crystals for THz-wave emitting devices.